U.S. patent number 4,180,138 [Application Number 05/838,283] was granted by the patent office on 1979-12-25 for vehicle having auxiliary drive mechanism.
This patent grant is currently assigned to Dana Corporation. Invention is credited to Dennis W. Shea.
United States Patent |
4,180,138 |
Shea |
December 25, 1979 |
Vehicle having auxiliary drive mechanism
Abstract
A vehicle has a forward mounted primary gasoline engine
operatively engaged with the front axle and its associated wheels.
The vehicle also has a rear mounted second motor drivingly engaged
with the rear axle which is normally a dead axle. The rear axle is
selectively drivingly engageable with the rear wheels which can
overrun the rear axle in both the forward and reverse directions.
The second motor is preferably an electric motor operable in two
directions but alternatively may be a hydraulic pump/motor. The
second motor, which may be driven by the primary motor or from an
independent power source such as a battery, is manually actuable by
the vehicle operator and automatically disengageable upon reaching
a predetermined speed.
Inventors: |
Shea; Dennis W. (Toledo,
OH) |
Assignee: |
Dana Corporation (Toledo,
OH)
|
Family
ID: |
25276723 |
Appl.
No.: |
05/838,283 |
Filed: |
September 30, 1977 |
Current U.S.
Class: |
180/65.25;
180/76; 180/245; 180/57; 180/243; 903/916 |
Current CPC
Class: |
B60K
6/48 (20130101); B60K 23/08 (20130101); B60K
6/52 (20130101); B60K 17/356 (20130101); B60L
50/15 (20190201); Y02T 10/7077 (20130101); Y02T
10/7072 (20130101); Y02T 10/6221 (20130101); Y02T
10/6265 (20130101); Y02T 10/62 (20130101); Y02T
10/7005 (20130101); Y02T 10/70 (20130101); Y10S
903/916 (20130101) |
Current International
Class: |
B60L
11/12 (20060101); B60L 11/02 (20060101); B60K
6/04 (20060101); B60K 6/00 (20060101); B60K
17/34 (20060101); B60K 17/356 (20060101); B60K
23/08 (20060101); B60L 011/14 (); B60L
011/12 () |
Field of
Search: |
;180/44M,44E,65R,65A,65C,76,54C,57 ;192/48.92 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Peters, Jr.; Joseph F.
Assistant Examiner: Smith; Milton L.
Attorney, Agent or Firm: Leonardi; Robert M.
Claims
I claim:
1. A vehicle comprising:
a first wheel and a first axle adapted for operative driving
engagement with said first wheel;
an internal combustion engine adapted for operative driving
engagement with said first axle;
generating means driven by said internal combustion engine;
a battery adapted to be charged by said generating means;
a second wheel, a second axle said second wheel being selectively
rotatable relative to said second axle and means for selectively
drivingly engaging said second axle with said second wheel;
an electric motor drivingly engaged with said second axle and
selectively drivingly engageable with said second wheel through
said second axle upon actuation of said electric motor, said
electric motor drivingly connected to said battery; and
means for selectively actuating and deactuating said electric
motor.
2. A vehicle as defined in claim 1 further comprising:
means for automatically disengaging said engaging means upon
deactuation of said electric motor.
3. A vehicle as defined in claim 1 wherein said electric motor is
operable in a forward direction mode and a reverse direction
mode.
4. A vehicle as defined in claim 3 further comprising a
transmission operatively drivingly connecting said engine and said
first wheel, said transmission having a reverse mode, and a back-up
light switch actuated when said transmission is in said reverse
mode, and means for switching said electric motor into said reverse
direction mode when said back-up light switch is actuated.
5. A vehicle as defined in claim 1 further comprising means for
automatically deactuating said electric motor when said motor
reaches a predetermined speed.
6. A vehicle as defined in claim 1 further comprising a throttle
for governing said engine, wherein said electric motor is
inoperable when said throttle is in its free standing state.
7. A vehicle as defined in claim 1 further comprising an ignition
switch actuatable for starting said engine, wherein said electric
motor is inoperable when said ignition switch is unactuated.
8. A vehicle as defined in claim 1 further comprising a brake
actuatable for braking said vehicle, wherein said electric motor is
inoperable when said brake is actuated.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to vehicles and more particularly
to vehicles having both a primary motor and an auxiliary motor.
As is well known, conventional vehicles such as passenger cars
sometimes become stalled in mud or snow or on ice when the drive
wheels, usually the rear wheels, lose traction. With the increasing
popularity of compact passenger vehicles, traction problems under
such adverse conditions have become more common. Compact and
subcompact vehicles are specially designed to be light in weight
and traction problems are therefore inherent. Furthermore, compacts
and subcompacts generally have small tires and wheels which, as is
well known, have relatively high rolling resistance. The increased
use of plastics and other lightweight materials in these and other
vehicles has made such traction problems even more widespread.
Traditional passenger cars having two-wheel drive are especially
susceptible to stalling under adverse road conditions. It has long
been known that full-time four-wheel-drive vehicles, such as
military or recreational vehicles, are especially adapted for
travel under adverse road conditions. Such full-time
four-wheel-drive vehicles are provide with front and rear drive
axles operatively and drivingly connected to a single mover such as
a gasoline engine. Vehicles have also been designed with part-time
four-wheel-drive capabilities. In these vehicles wheel locks or
clutches are manually or automatically selectively engageable to
transform the vehicle from a two-wheel-drive to a four-wheel-drive
system. Although full or part-time four wheel-drive vehicles have
proved highly successful in specific situations, the large drive
mechanisms used in these vehicles are generally unsuitable in size
and weight for the presently popular compact and subcompact
vehicles.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a vehicle
having a lightweight auxiliary drive system.
It is a further object of the present invention to provide a
vehicle having a primary mover and an auxiliary mover.
It is still a further object of the present invention to provide a
vehicle which is selectively driveable through two axles.
These and other objects of the present invention which will become
apparent from the following detailed description are achieved by a
vehicle having a primary mover adapted for driving engagement with
a first axle which is drivingly engaged with a first wheel. The
vehicle further comprises a secondary mover drivingly engaged with
a second axle which is selectively drivingly engageable with a
second wheel. Preferably, the secondary mover comprises an electric
motor which is operable in two directions. The secondary mover may
be manually actuatable by the vehicle operator and automatically
disengageable upon the vehicle reaching a predetermined speed. The
secondary mover may be driven by the primary mover or may be
operable from an independent power source such as a battery. The
second axle is a dead axle when the secondary mover in inoperative.
The second wheel therefore comprises means for overrunning the
second axle, preferably in two directions.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of a vehicle having the auxiliary drive
system of the present invention, a portion of the vehicle being
broken away to show the chassis components.
FIG. 2 is a rear elevation view of the rear wheel and axle assembly
of the vehicle of FIG. 1.
FIG. 3 is a cross-sectional elevation view of the right rear wheel
end assembly of the axle in FIG. 2.
FIG. 4 is a schematic diagram of an electrical circuit for the
auxiliary drive system of the present invention.
DETAILED DESCRIPTION OF A PRESENTLY PREFERRED EMBODIMENT
Referring to FIG. 1, a subcompact passenger vehicle 10 is shown
having a frame 12 upon which is secured the vehicle body 14. The
vehicle 10 has a forward mounted primary mover 20 which is a
gasoline engine in the presently preferred embodiment. Power for
starting the engine 20 is supplied by a twelve volt battery 18.
Much of the electrical system for starting the engine 20, as for
instance the starter and associated wiring, has not been
illustrated in FIG. 1 as it is well known in the art. An electrical
generator 19, driven by the engine 20, is adapted to recharge the
battery 18 through a voltage regulator 21 and to supply electrical
power to various electrical accessories in the vehicle such as a
radio, heater, lights, etc.
In the presently preferred embodiment, a manual transmission 22 is
drivingly connected to the engine output shaft (not shown). It
should be noted, however, that the present invention may readily be
utilized with a vehicle having an automatic transmission. A
transmission output shaft 23 extends downwardly from the bottom of
the transmission 22 into a right angle differential unit 24. Right
and left front drive axles 25 and 26 are drivingly engaged with the
transmission output shaft 23 through the drive unit 24 and with the
front drive wheels 27. The transmission 22 permits both forward and
reverse drive of the axles 25 and 26 as is well known in the art.
The mechanism for steering the front wheels 27 is not illustrated
in FIG. 1 as it too is well known in the art.
As can more clearly be seen in FIG. 2 the vehicle 10 has a
selectively drivable rear axle assembly 34 contained within a rear
axle housing 36 which extends between the right and left rear
wheels 37 and 37'.
The rear axle housing 36 is bent upward near the center of the
vehicle to provide additional ground clearance, but it should be
understood that a straight axle is within the scope of the present
invention. The right side of the axle assembly 34 includes right
axle shafts 35, 48 and 50 (see FIG. 3) drivingly connected in
series by universal joints 46 and 47. The left side of the axle
assembly 34 comprises an identical series of axle shafts, including
shaft 35', which operate in a manner similar to the right side of
the axle assembly.
A secondary, electric motor 40 is rigidly affixed to the rear
portion of the frame 12 above the rear axle assembly 34 by brackets
39. The frame 12 is connected to the rear axle housing 36 by rear
springs 33 and 33' which act to cushion the frame and the secondary
mover 40 from jolts due to adverse road conditions.
A telescoping slip shaft 42 (see also FIG. 1) extends from the
electric motor 40 into a right angle drive unit 44. The shaft 42 is
adapted to accommodate any variation in distance between the motor
40 and the axle housing 36, such as those caused by adverse road
conditions. The shaft 42 should be designed to telescope a distance
as required to accommodate anticipated axle movement.
The drive unit 44 includes a housing 45 integral with the axle
housing 36. The drive unit 44 comprises a worm gear 41 rigidly
connected to the axle shafts 35 and 35'. The worm gear 41 is
thereby adapted to drive both the right and left wheels 37 and 37'
as will be described. The unit 44 also comprises a worm 43
operatively drivingly engaged with the worm gear 41. The worm 43 is
affixed to the telescoping shaft 42 which extends from the motor 40
and is adapted to be driven thereby.
It should be noted that other types of drive systems can easily be
adapted to replace the drive unit 44. For instance, other types of
gearing such a spiroid, helicoid, or planetary gearing could be
used, as well as belt or chain drive systems either alone or in
combination with gearing. The worm and worm gear system disclosed
is presently preferred because of its high torque ratio.
When the electric motor 40 is inoperative, the entire axle assembly
34, including the axle shafts 35, 35', 48 and 50, remains
stationary. In other words, the axle assembly 34 is normally a
"dead" axle. The associated rear wheel end assemblies must
therefore be adapted to permit free rotation of the rear wheels 37
and 37' when the rear axle is stationary.
Referring to FIG. 3, the right end axle shaft 50 has right hand
threads 52 near its outer end portion. The wheel end assembly 53
includes a stationary member 54 which is rigidly secured to the
axle housing 36 and which contains a set of bearings 49 for
radially aligning the axle shaft 50.
A threaded steel input clutch member 55 is screwed onto the
threaded outer portion of the axle shaft 50. The input clutch 55
has two frusto conical surfaces 59 and 60, each tapering away from
the other. The stationary member 54 has an annular protuberance 51
extending axially outwardly toward the wheel 37. An annular drag
spring 56 is rigidly secured to the protuberance 51 and is slidably
engaged with an annular axially inward extension 57 of the input
clutch member 55.
A two piece output clutch is rigidly connected to the right rear
wheel by means (such as bolting) well known in the art. The output
clutch members 58 and 68 are held rigidly together by a clip 78.
Together the members 58 and 68 define a cavity 61 in which the
input clutch member 55 is contained. The output clutch member
cavity 61 is defined in part by two frusto conical clutching
surfaces. Surface 69 on clutch member 68 and surface 70 on member
58 are adapted for frictional engagement with the input clutch
member surfaces 59 and 60, respectively. The output clutch is made
in two components 58 and 68 to permit insertion of the input clutch
55 within the output clutch cavity 61. Output clutch member 58 also
houses a bearing assembly 71 for radially aligning the shaft 50.
The housing member 36 houses a bearing assembly 79 for radially
aligning the output clutch member 58.
When the axle shaft 50 is driven in a forward direction (as
indicated by the arrow 61 in FIG. 3) the input clutch member 55 is
held rotationally stationary by the drag spring 56. The clutch
member 55 is therefore screwed outwardly (rightwardly as viewed in
FIG. 3) on the input shaft 50 towards the wheel 37 until the input
clutching surface 60 frictionally engages the output clutching
surface 70. At this point the input clutch member 55 is locked
between the input shaft 50 and the output clutch member 58. The
locked driving relationship between these members exists as long as
the output clutch member 58 continues to drive the wheel 37. In
this condition the drag spring force is overcome by the driving
forces and the input clutch rotates with the shaft 50 and wheel
37.
If the driving force applied by the axle shaft 50 should cease, as
for example by stopping the auxiliary motor 40 or by rotating the
wheel 37 faster than the rotation on the input shaft 50, the wheel
37 is free to overrun the input shaft 50. When the wheel 37
overruns the shaft 50, the output clutch member 58 turns the input
clutch member 55 in the forward direction 61 relative to the shaft
50 because of the frictional engagement of the clutch members 55
and 58. The output clutch member 58 therefore moves the input
clutch member 55 axially inwardly on the threaded shaft 50,
disengaging the clutch surfaces 60 and 70.
As the input shaft 50 continues to rotate, the drag spring 56 holds
the input clutch member 55 rotationally stationary causing it to
reverse its direction and move axially outwardly toward the wheel
37, thereby re-engaging the output clutch member 58. If the
rotational speed of the input shaft 50 is less than that of the
output clutch member 58, the input member 55 will be bumped out of
engagement each time the drag spring 56 and the shaft 50 attempt to
engage the surfaces 60 and 70. If the wheel 37 slows to a speed
less than that of the shaft 50, the clutch surfaces 60 and 60 are
re-engaged as previously described and the wheel is again
driven.
When the auxiliary motor is stopped for any reason, the input shaft
50 will also stop and the wheel 37 will overrun the input shaft 50
as just described. As the wheel 37 continues to rotate it
disengages the input clutch member 55 from the output clutch member
58. Because the shaft 50 is stopped, the drag spring 56 retains the
clutch member 55 between the surfaces 69 and 70 of the output
member 58 and no bumping occurs between the members 55 and 58.
A reverse rotation of the axle shaft 50 causes engagement of the
clutch surfaces 59 and 69 whereby the wheel 37 is driven in the
reverse direction. Overruning in the reverse direction is
accomplished similarly to that in the forward direction.
It should be noted that the wheel end assemblies will be operative
regardless of whether the wheel end shafts such as 50 have right or
left hand threads, as this will only change which clutching
surfaces are engaged for forward and reverse operation. It should
also be noted that the wheel end assemblies 53 and 53' are
essentially identical and simultaneously drive the wheels 37 and
37', respectively. Because of the overruning capabilities of each
assembly 53 and 53', no differential gearing is necessary, as the
slow wheel will always be driven while the faster wheel
overruns.
The preferred auxiliary motor circuit is provided with means for
disengaging the input clutch member 55 from the output clutch
members 58 or 68 when the auxiliary motor 40 is deactivated.
Disengagement of the clutch members is accomplished by momentarily
rotating the wheel end shaft 50 in the direction opposite that in
which it was driving. This brief rotation, one-quarter turn for
example, in the opposite direction assures that the input clutch
member 55 frees itself from locking frictional engagement with the
output clutch. Such a locking condition could cause the entire
system to be backdriven, possibly resulting in damage to the
system. The presently preferred electrical circuit for
accomplishing this disengagement will be described hereinafter.
Referring again to FIG. 1, the auxiliary electric motor 40 is
electrically connected directly to the battery 18. It is therefore
possible for the auxiliary motor 40 to be driven for short periods
by the battery 18 without the engine 20 being in operation. An
auxiliary motor on/off switch 66 interrupts the electrical line 62
and is conveniently located in the vehicle operator's compartment.
It is sufficient for most anticipated situations that the battery
18 be operative to move the vehicle at a speed of about 5 m.p.h.
for a distance of up to two to three hundred yards before requiring
a recharge. However, if the engine 20 is running, the generator 19,
through the voltage regulator 21, continuously recharges the
battery 18 and the electric motor 40 is in effect driven by the
primary mover. Alternatively, the electric motor 40 may be
electrically connected directly to the voltage regulator 21 and
generator 19 by the wires 64 shown in phantom in FIG. 1. In this
alternative mode the secondary mover 40 can be activated only when
the primary mover 20 is in operation.
In the presently preferred embodiment the auxiliary drive motor 40
is a 12 Volt DC reversible split series electric motor. It may be
run in either the forward or reverse direction. The motor 40 is
controlled by a relay logic system using a multitude of relays,
switches, diodes, capacitors and system status lights. A preferred
electrical circuit for operation of the auxiliary motor system of
the presently preferred embodiment is illustrated in FIG. 4.
In FIG. 4, all relays are depicted as coils and are denoted "R"
(e.g. R-1, R-2, etc.). Each relay is operative to act upon a
corresponding set of contact points denoted "CR" (e.g., CR-1, CR-2,
etc.).
Power to the electric motor 40 is supplied from the positive
terminal of a 12-volt buss battery. To activate the auxiliary
electric motor 40, the ON SWITCH must momentarily be depressed to
complete the circuit. This activates the SYSTEM-ON LIGHT. Current
from the battery flows through relay R-1 which closes the normally
open contact CR-1 and allows current from the battery to flow
through relays R-2 and R-3. Normally open contact CR-2 is therefore
closed, bypassing the ON SWITCH after it springs to its normally
open position. The auxiliary system can thereby operate without the
ON SWITCH being closed throughout operation. Current through relay
R-3 simultaneously closes normally open contact CR-3 and opens
normally closed contact CR-3' which effects a charging of the JOG
AND SWITCH capacitor. The operation of the JOG AND SWITCH portion
of the circuit will be described hereinafter.
Before current can reach the motor 40, it must pass through the OFF
SWITCH and the MOTOR OVERSPEED SWITCH, which are both normally
closed, to the normally open contact CR-9. Contact CR-9 is closed
by relay R-9 when it is activated by current passing from the
battery through the OVER-TEMPERATURE SWITCH. The OVER-TEMPERATURE
SWITCH is normally closed unless the motor 40 overheats. Current
must also pass through normally closed contact CR-5 which may be
opened by relay R-5 if the vehicle brake pedal is depressed, or by
closing the CLUTCH SWITCH. In a vehicle having an automatic
transmission the CLUTCH SWITCH would of course be omitted.
On its path to the auxiliary motor 40 current must pass through the
THROTTLE SWITCH, which is closed by a slight depressing of the
throttle, to the normally open contact CR-10. Relay R-10 closes the
contact CR-10 when the IGNITION SWITCH is closed by the vehicle
operator turning the vehicle ignition to the "on" position.
With all of the previously mentioned switches and contacts closed
the current can reach the contacts CR-6 which is normally closed
and CR-6' which is normally open. When the electric motor 40 is
operated in the forward mode the contact CR-6 remains closed with
the current thereby passing through the diodes D-1 and D-2. Current
passing through diode D-1 charges the REVERSE JOG capacitor.
Current passing through the diode D-2 activates relay R-8 which
closes the contact CR-8. Current is then permitted to pass through
relay MR-F which closes contact CMR-F, thereby completing a current
path from the battery to the FORWARD terminal of the motor 40.
To operate the electric motor 40 in the reverse mode, the manual
transmission 22 is shifted into reverse. The reverse setting in the
transmission closes the BACKUP LIGHT SWITCH, thereby activating the
relay R-6 which opens the contact CR-6 and closes the contact
CR-6'. Current is therefore prevented from passing through diodes
D-1 and D-2 and is permitted to pass through the diodes D-3 and
D-4. Current passing through diode D-3 charges the FORWARD JOG
capacitor. Current passing through the diode D-4 activates the
relay R-7 which closes the normally open contact CR-7. The relay
MR-R is therefore activated, which closes the contact CMR-R and
completes the circuit to the REVERSE terminal of the electric motor
40 and drives the motor in the reverse direction.
Several safety features are built into the auxiliary motor circuit
as illustrated in FIG. 4. For example, the IGNITION SWITCH must be
turned on before the system can be activated. Furthermore, as
previously described, the operator must be touching the accelerator
pedal to close the THROTTLE SWITCH and must be partially engaging
the clutch to open the CLUTCH SWITCH. If any of these switches
change position during operation of the auxiliary motor 40, current
flow to the motor will immediately cease. It can therefore be seen
that the vehicle operator must be in the driver's seat and poised
for operation of the vehicle before the system can be activated.
The safety features alleviate the problems of an inadvertent
switching on of the auxiliary system which may cause an accident if
the vehicle is in a location with narrow clearance, such as a
garage or in heavy traffic.
Further safety factors are also built into the auxiliary motor
circuit. For example, the centrifugal MOTOR OVERSPEED switch breaks
the circuit, therefore cutting off current flow to the motor 40,
when the motor reaches a predetermined speed. Heating of the motor
over a predetermined temperature causes the OVER-TEMPERATURE SWITCH
to open, thereby deactivating the relay R-9 which closes the
contact CR-9', illuminating the OVER-TEMPERATURE LIGHT, and opening
contact CR-9 thereby terminating current flow to the motor 40.
As previously noted, when the electric motor is activated in either
the forward or reverse direction, the REVERSE JOG or the FORWARD
JOG capacitor, respectively, is charged. Current ceases to flow
through relay R-3, when the circuit leading to the electric motor
40 is broken, as for example by the OVERSPEED SWITCH,
OVERTEMPRATURE SWITCH, or OFF SWITCH. Contact CR-3 therefore
returns to its normally open position while contact CR-3' returns
to its normally closed position. The charged JOG AND SWITCH
capacitor discharges through the relay R-4 which momentarily closes
the normally open contacts CR-4. The charged REVERSE JOG or FORWARD
JOG capacitor therefore discharges through the relay R-7 or R-8,
respectively. The pulse of current passing through the relays R-7
or R-8 momentarily closes the contact CR-7 or CR-8, respectively.
This permits a pulse of current to momentarily drive the electric
motor 40 in the reverse or the forward direction, respectively,
thereby disengaging the wheel end clutch assembly as previously
described.
Under actual driving conditions, if front wheel of the vehicle 10
of the present invention is stalled on ice for example, the
auxiliary system may be utilized. To activate the system the driver
leaves the ignition switch on, slightly touches the throttle, and
begins to release the clutch. He then depresses the auxiliary
SYSTEM-ON SWITCH, with the SYSTEM-ON LIGHT indicating such, which
fully connects the circuit of the auxiliary drive motor 40.
Rotation of the motor 40 then begins in the selected direction with
the motor 40 driving the rear axle as previously described.
When the vehicle is out of the road incumberance, the auxiliary
motor 40 may be deactivated by the OFF SWITCH which breaks the
auxiliary motor circuit shown in FIG. 4. If the driver fails to
manually deactivate the system, the MOTOR OVERSPEED SWITCH
automatically breaks the circuit when the auxiliary motor reaches a
predetermined speed. The BRAKE SWITCH will also deactivate the
system upon a slight touching of the brake pedal.
It should further be noted that the auxiliary system of the present
invention may be modified such that the auxiliary motor 40 is
automatically activated upon slippage of the drive wheels. Such an
automatic auxiliary drive system requires means for determining
when the front drive wheels are slipping. One such means is a wheel
speed sensing device such as a magnetic pickup 70 (illustrated in
phantom in FIG. 1) which "reads" equally circumferentially spaced
teeth, ridges or other surface deviations 71 on the drive wheel 27
or on a ring attached thereto. Output from the sensor is fed
through a logic portion 72 of the system which compares wheel speed
changes with a predetermined programed permissible speed variation
range. Upon deviation from the permissible range the logic 72
activates a switch 73 which connects the wires 62, thereby
completing the circuit from the battery 18 to the auxiliary motor
40. The logic 72 is also adapted to open the switch 73 when the
wheel slip condition is terminated. Wheel speed sensing devices as
described are presently utlized on anti-skid braking systems which
are presently available for passenger automobiles and trucks. Such
anti-skid braking systems could easily be adapted to automatically
activate the auxiliary motor system of the present invention.
It should be noted that other types of auxiliary motors such as
hydraulic pump/motors may be utilized in the vehicle of the present
invention. Hydraulic pump/motors are well known in the art and have
often been utilized in systems involving vehicle power
transmission. Hydraulic auxiliary movers generally derive their
power from the primary motor and thereby may only be utilized in
applications when such derivative power is sufficient. However,
hydraulic pump/motors may be switched from a forward drive
direction to reverse drive direction merely by the switching of
hydraulic valve.
The structure previously described has been for the purpose of
illustrating a presently preferred embodiment of the invention. It
should be understood that many other modifications or alterations
may be made without departing from the spirit and the scope of the
invention as set forth in the appended claims.
* * * * *